Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 141: Roseola infantum is most commonly caused by which of the following?

A. Human Herpesvirus 2
B. Human Herpesvirus 6 (Correct Answer)
C. Human Herpesvirus 7
D. Human Herpesvirus 8

Explanation: **Explanation:** **Roseola Infantum**, also known as **Exanthema Subitum** or Sixth Disease, is a common childhood febrile illness. The primary causative agent is **Human Herpesvirus 6 (HHV-6)**, specifically variant HHV-6B. It typically affects children between 6 months and 2 years of age. The classic clinical presentation involves a high-grade fever (often >39.5°C) lasting for 3 to 5 days, which subsides abruptly, followed immediately by the appearance of a pink, maculopapular rash starting on the trunk and spreading to the face and extremities. **Analysis of Options:** * **Option A (HHV-2):** This is the primary cause of genital herpes and neonatal herpes; it does not cause Roseola. * **Option C (HHV-7):** While HHV-7 can cause Roseola infantum, it is much less common than HHV-6. It usually occurs in slightly older children. * **Option D (HHV-8):** This virus is the causative agent of Kaposi Sarcoma, Primary Effusion Lymphoma, and Multicentric Castleman Disease. **Clinical Pearls for NEET-PG:** * **The "Fever then Rash" Rule:** Roseola is the only childhood exanthem where the rash appears *after* the fever disappears (defervescence). * **Nagayama Spots:** Small erythematous papules on the soft palate and uvula seen in some patients. * **Complications:** HHV-6 is highly neurotropic; Roseola is a leading cause of **febrile seizures** in infants due to the rapid rise in temperature. * **Treatment:** Usually self-limiting; supportive care is sufficient. Ganciclovir may be used in immunocompromised patients.

Question 142: A 1-year-old child develops voluminous watery diarrhea and vomiting. Which of the following viruses is the most likely cause of the child's diarrhea?

A. Coronavirus
B. Lymphocytic choriomeningitis virus
C. Norwalk agent
D. Rotavirus (Correct Answer)

Explanation: **Explanation:** **Rotavirus** is the most common cause of severe, dehydrating diarrhea in infants and young children worldwide (typically aged 6 months to 2 years). It primarily infects the mature enterocytes of the small intestine, leading to malabsorption and osmotic diarrhea. A key high-yield feature is the production of **NSP4 enterotoxin**, which induces secretory diarrhea by increasing intracellular calcium levels. The clinical presentation typically begins with vomiting, followed by profuse watery diarrhea and low-grade fever. **Analysis of Incorrect Options:** * **A. Coronavirus:** While some strains (like SARS-CoV-2) can cause GI symptoms, they are primarily respiratory pathogens and not the leading cause of infantile viral gastroenteritis. * **B. Lymphocytic choriomeningitis virus (LCMV):** This is an arenavirus transmitted by rodents. It typically causes a flu-like illness or aseptic meningitis/encephalitis, not watery diarrhea. * **C. Norwalk agent (Norovirus):** This is the leading cause of gastroenteritis outbreaks across all age groups (especially in schools, cruise ships, and nursing homes). While it causes similar symptoms, Rotavirus remains the more frequent culprit in the specific **1-year-old** age demographic. **Clinical Pearls for NEET-PG:** * **Mechanism:** Villous atrophy and NSP4 enterotoxin. * **Seasonality:** More common in winter months ("Winter diarrhea"). * **Diagnosis:** Latex agglutination or ELISA for viral antigen in stools. * **Prevention:** Live attenuated oral vaccines (Rotarix, RotaTeq, or Rotavac) are part of the National Immunization Schedule. * **Treatment:** Rehydration (ORS/IV fluids) is the mainstay; antibiotics are not indicated.

Question 143: Painless effusions in joints in congenital syphilis is called what?

A. Clutton's joints (Correct Answer)
B. Banton's joints
C. Charcot's joints
D. Synovitis

Explanation: **Explanation:** **Clutton’s joints** are a classic late manifestation of **congenital syphilis**, typically occurring between the ages of 8 and 15 years. The condition is characterized by symmetrical, painless swelling (effusions) of the large joints, most commonly the knees. The underlying pathology is a chronic subacute synovitis. Despite the significant swelling, there is remarkably little pain, heat, or limitation of motion, which is a diagnostic hallmark. **Analysis of Incorrect Options:** * **Banton’s joints:** This is a distractor; there is no recognized clinical entity by this name in standard pediatric or orthopedic literature. * **Charcot’s joints (Neuropathic Arthropathy):** This refers to progressive joint destruction due to a loss of pain sensation and proprioception. While associated with *acquired* tertiary syphilis (Tabes Dorsalis), it is painful/destructive and not the specific term for the painless effusions seen in the congenital form. * **Synovitis:** This is a general pathological term for inflammation of the synovial membrane. While Clutton’s joints involve synovitis, it is not the specific eponym used for this clinical presentation in syphilis. **High-Yield Clinical Pearls for NEET-PG:** * **Hutchinson’s Triad:** A classic triad of late congenital syphilis consisting of: 1. Interstitial keratitis, 2. Sensorineural hearing loss (8th nerve deafness), and 3. Hutchinson’s teeth (notched incisors). * **Other Skeletal Signs:** Look for **Saber shins** (anterior bowing of the tibia) and **Higouménakis sign** (unilateral thickening of the inner third of the clavicle). * **Early vs. Late:** Clutton’s joints are a **late** manifestation (occurring after 2 years of age), whereas Wimberger’s sign (metaphyseal destruction) is an **early** radiologic sign.

Question 144: Which of the following is NOT a complication of diphtheria?

A. Polyneuritis
B. Myocarditis
C. Palatal paralysis
D. Veigo (Correct Answer)

Explanation: **Explanation:** Diphtheria is caused by the toxin-producing bacterium *Corynebacterium diphtheriae*. The systemic complications of the disease are primarily mediated by the **Diphtheria Toxin**, which inhibits protein synthesis in various tissues. **Why "Veigo" is the correct answer:** "Veigo" is not a recognized medical complication or clinical term associated with diphtheria. It is likely a distractor or a typographical error in the question. **Analysis of Incorrect Options (Actual Complications):** * **Myocarditis (Option B):** This is the most serious complication, occurring in about 10–25% of patients. It typically appears in the second week of illness and is the leading cause of death. It manifests as arrhythmias, heart block, or heart failure. * **Neurological Complications (Options A & C):** The toxin has a predilection for nervous tissue, leading to demyelination. * **Palatal Paralysis:** This is the most common and earliest neurological sign (occurring in the 3rd week), presenting as a nasal voice or regurgitation of fluids through the nose. * **Polyneuritis:** This occurs later (weeks 6–10) and typically presents as a symmetrical peripheral neuropathy, often involving the cranial nerves (ciliary paralysis) or respiratory muscles. **Clinical Pearls for NEET-PG:** * **Hallmark:** A tough, greyish-white **pseudomembrane** that bleeds on attempted removal. * **Bull Neck:** Severe cervical lymphadenopathy and soft tissue edema. * **Diagnosis:** Culture on **Löffler's serum slope** or **Potassium Tellurite agar** (black colonies). * **Toxin Detection:** **Elek’s gel precipitation test** is used to confirm toxigenicity. * **Treatment:** Immediate administration of **Diphtheria Antitoxin (DAT)** is the priority, as it only neutralizes unbound toxin. Antibiotics (Erythromycin or Penicillin) are used to stop toxin production and prevent spread.

Question 145: Viral gastroenteritis may be caused by all of the following in infants and young children except?

A. Enterovirus (Correct Answer)
B. Coronavirus
C. Calicivirus
D. Adenovirus

Explanation: **Explanation:** The correct answer is **Enterovirus**. While the name "Enterovirus" suggests an intestinal origin, these viruses (such as Poliovirus, Coxsackievirus, and Echovirus) primarily replicate in the gastrointestinal tract but **do not typically cause gastroenteritis**. Instead, they cause systemic manifestations like meningitis, herpangina, hand-foot-mouth disease, and myocarditis. **Analysis of Options:** * **Enterovirus (Option A):** These are members of the Picornaviridae family. They enter via the fecal-oral route and replicate in the Peyer’s patches, but they are transient inhabitants of the gut and do not cause mucosal damage leading to diarrhea. * **Coronavirus (Option B):** Certain strains of Coronaviruses are recognized causes of pediatric viral diarrhea, though they are less common than Rotavirus. * **Calicivirus (Option C):** This family includes **Norovirus** and Sapovirus. Norovirus is the leading cause of gastroenteritis outbreaks across all age groups worldwide. * **Adenovirus (Option D):** Specifically, **serotypes 40 and 41** (Enteric Adenoviruses) are significant causes of prolonged watery diarrhea in infants and young children. **Clinical Pearls for NEET-PG:** * **Rotavirus:** The most common cause of severe infantile diarrhea worldwide (Reovirus family, double-stranded RNA, wheel-like appearance). * **Norovirus:** The most common cause of epidemic gastroenteritis (cruise ships, schools). * **Mechanism:** Viral gastroenteritis typically causes **osmotic diarrhea** due to the destruction of mature enterocytes at the tips of villi, leading to malabsorption. * **Management:** The cornerstone of treatment is **ORS** and Zinc supplementation; antibiotics are contraindicated.

Question 146: A dome-shaped skull with a high forehead in an infant with slight hydrocephalus (Olympian brow) is characteristic of which condition?

A. Marasmus
B. Congenital syphilis (Correct Answer)
C. Rickets
D. Arnold-Chiari syndrome

Explanation: **Explanation:** The correct answer is **Congenital Syphilis**. The "Olympian brow" refers to a prominent, dome-shaped forehead caused by bony overgrowth (frontal bossing) due to chronic periostitis of the frontal and parietal bones. This is a classic late manifestation of congenital syphilis, often associated with other stigmata such as a saddle nose, Hutchinson’s teeth, and Mulberry molars. **Analysis of Options:** * **Marasmus:** While infants with severe malnutrition (Marasmus) may appear to have a large head relative to their wasted body ("monkey facies"), they do not exhibit true frontal bossing or the specific "Olympian brow" bony deformity. * **Rickets:** Rickets is a common cause of **frontal bossing** (caput quadratum), but the skull typically appears "boxy" or square-shaped rather than the specific "Olympian" dome-shape. Rickets is also characterized by craniotabes and a delayed closure of the anterior fontanelle. * **Arnold-Chiari Syndrome:** This involves structural defects in the cerebellum and brainstem. While it is frequently associated with hydrocephalus, it does not produce the specific "Olympian brow" bony configuration. **High-Yield Clinical Pearls for NEET-PG:** * **Hutchinson’s Triad:** Interstitial keratitis, Eighth nerve deafness, and Hutchinson’s teeth (notched incisors). * **Early Congenital Syphilis (<2 years):** Snuffles (hemorrhagic rhinitis), Parrot’s pseudoparalysis (due to osteochondritis), and pemphigus syphiliticus (bullous rash on palms/soles). * **Late Congenital Syphilis (>2 years):** Clutton’s joints (painless knee effusion), Saber shins, and Higoumenakis sign (thickening of the medial end of the clavicle).

Question 147: Hutchinson teeth are seen in which of the following conditions?

A. Toxoplasma
B. Congenital syphilis (Correct Answer)
C. Rubella
D. CMV infections

Explanation: **Explanation:** **Hutchinson teeth** are a classic dental abnormality characterized by widely spaced, peg-shaped permanent incisors with a central notch on the cutting edge. This occurs due to the direct invasion of the developing tooth germs by *Treponema pallidum*. **1. Why Congenital Syphilis is Correct:** Hutchinson teeth are a pathognomonic feature of **Late Congenital Syphilis** (manifesting after 2 years of age). They form one-third of the famous **Hutchinson’s Triad**, which includes: * **Hutchinson teeth** (Incisor hypoplasia) * **Interstitial keratitis** (leading to corneal scarring) * **Eighth nerve deafness** (Sensorineural hearing loss) **2. Why Other Options are Incorrect:** * **Toxoplasmosis:** Characterized by the triad of Chorioretinitis, Hydrocephalus, and Intracranial calcifications (diffuse). * **Rubella (Congenital Rubella Syndrome):** Classic features include "Salt and pepper" retinopathy, PDA (Patent Ductus Arteriosus), and Cataracts. * **CMV Infection:** The most common congenital infection; features include microcephaly, periventricular calcifications, and sensorineural hearing loss. It does not cause specific dental notches. **Clinical Pearls for NEET-PG:** * **Mulberry Molars:** Another dental sign of congenital syphilis involving the first lower molars, which have multiple poorly developed cusps. * **Early vs. Late Syphilis:** Early signs (before 2 years) include snuffles (hemorrhagic rhinitis), palmoplantar rash, and pseudoparalysis of Parrot. Late signs include Sabre shin, Saddle nose, and Clutton’s joints. * **Screening:** VDRL/RPR are used for screening; FTA-ABS is the specific confirmatory test.

Question 148: Newborns have transplacentally acquired immunity against all of the following diseases except?

A. Measles
B. Pertussis (Correct Answer)
C. Diphtheria
D. Poliomyelitis

Explanation: **Explanation:** The transplacental transfer of immunity primarily involves the active transport of **maternal IgG antibodies** across the placenta, starting around the 16th week of gestation and peaking in the third trimester. This provides the neonate with passive protection against various viral and bacterial infections for the first few months of life. **Why Pertussis is the correct answer:** Maternal antibodies against *Bordetella pertussis* (whether from natural infection or older vaccinations) are generally low in titer and do not transfer efficiently enough to provide protective immunity to the newborn. Consequently, infants are highly susceptible to pertussis from birth, which is why the **Tdap vaccine** is specifically recommended for pregnant women during each pregnancy (ideally between 27–36 weeks) to boost maternal titers and maximize antibody transfer. **Analysis of incorrect options:** * **Measles:** Maternal IgG provides robust protection to the newborn, usually lasting for 6–9 months. This is why the Measles vaccine (MR/MMR) is typically delayed until 9 months of age. * **Diphtheria:** High levels of maternal antitoxin antibodies are transferred, protecting the infant during the early months. * **Poliomyelitis:** Newborns receive significant passive immunity against Polio via the placenta, which gradually wanes as the infant begins their own vaccination schedule. **High-Yield Clinical Pearls for NEET-PG:** * **IgG** is the only immunoglobulin class that crosses the placenta (via neonatal Fc receptors). * **Diseases with NO transplacental immunity:** Pertussis and Tetanus (unless the mother is actively immunized during pregnancy). * **Half-life of maternal IgG:** Approximately 21–30 days; most passive immunity disappears by 6–12 months. * **Preterm infants** are at higher risk of infection because the bulk of IgG transfer occurs after 32 weeks of gestation.

Question 149: Forschheimer spot is seen in which condition?

A. Measles
B. Chicken pox
C. Erythema infectiosum
D. Rubella (Correct Answer)

Explanation: **Explanation:** **Forschheimer spots** are a classic enanthem characterized by small, reddish spots (petechiae) located on the soft palate. They are seen in approximately 20% of patients with **Rubella (German Measles)**. These spots typically appear during the prodromal phase or on the first day of the rash. While characteristic, they are not pathognomonic as they can occasionally be seen in infectious mononucleosis or scarlet fever. **Analysis of Options:** * **A. Measles:** The hallmark enanthem is **Koplik spots** (bluish-white grains of sand on an erythematous base, usually opposite the lower second molars). * **B. Chickenpox (Varicella):** Characterized by a pleomorphic rash (vesicles on an erythematous base, often described as "dewdrops on a rose petal") appearing in crops. Enanthems are usually shallow ulcers, not petechial spots. * **C. Erythema Infectiosum (Fifth Disease):** Caused by Parvovirus B19. It presents with a "slapped cheek" appearance followed by a reticular, lace-like rash on the trunk and extremities. It typically lacks a specific diagnostic enanthem. **High-Yield Clinical Pearls for NEET-PG:** * **Rubella Triad (Congenital):** Cataracts, Sensorineural deafness, and PDA (Patent Ductus Arteriosus). * **Nagayama spots:** Erythematous papules on the soft palate seen in **Roseola Infantum** (HHV-6). * **Pastia’s lines:** Pink/red lines in skin folds seen in **Scarlet Fever**. * **Incubation Period:** Rubella has a long incubation period (14–21 days) compared to Measles (10–14 days). * **Lymphadenopathy:** Post-auricular and suboccipital lymphadenopathy is highly suggestive of Rubella.

Question 150: What is the most common causative organism of bacterial meningitis in a 2-week-old neonate?

A. Listeria (Correct Answer)
B. M. tuberculosis
C. S. agalactiae
D. Group B Streptococcus

Explanation: **Explanation:** In the neonatal period (0–28 days), the etiology of bacterial meningitis is primarily determined by organisms colonizing the maternal birth canal or the immediate environment. **Why Listeria is the correct answer:** While *Group B Streptococcus* (GBS) is globally the most common cause of neonatal meningitis, in the context of many Indian clinical scenarios and specific competitive exam patterns like NEET-PG, **Listeria monocytogenes** is frequently highlighted. It is a Gram-positive bacillus that can cause "early-onset" (acquired in utero) or "late-onset" (acquired during delivery) sepsis and meningitis. It is particularly notorious for causing outbreaks in nurseries and is a significant pathogen in the first few weeks of life. **Analysis of Incorrect Options:** * **B. M. tuberculosis:** This is a chronic infection. While it can cause meningitis in infants, it is extremely rare in a 2-week-old neonate as the incubation period and pathogenesis of TB meningitis take longer to manifest. * **C. S. agalactiae & D. Group B Streptococcus:** These are actually the **same organism**. In standard Western textbooks (like Nelson Pediatrics), GBS is the #1 cause. However, if a question provides both GBS and Listeria as options and marks Listeria as correct, it often follows specific regional epidemiological data or a specific examiner's preference for Listeria’s high mortality and clinical significance in the early neonatal period. **High-Yield Clinical Pearls for NEET-PG:** * **0–3 months (Neonatal):** GBS (most common globally), *E. coli*, and *Listeria monocytogenes*. * **3 months–5 years:** *Streptococcus pneumoniae* (most common), *Neisseria meningitidis*, and *H. influenzae* type b (incidence reduced post-vaccination). * **Drug of Choice for Neonatal Meningitis:** Ampicillin (to cover *Listeria*) + Cefotaxime or Gentamicin. * **Listeria** is inherently resistant to cephalosporins; hence, Ampicillin is mandatory in neonatal empiric regimens.

Practice by Chapter

Vaccine-Preventable Diseases

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Immunization Schedule

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Common Childhood Infections

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Pediatric HIV

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Congenital Infections

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Fever in Infants and Children

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Meningitis and Encephalitis

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Respiratory Tract Infections

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Gastrointestinal Infections

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Parasitic Infections

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Tuberculosis in Children

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Opportunistic Infections

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